Happy Birthday Frank!
The 71 Johnson does have the vibration dampers, one on each side of the powerhead.
This is not a retrofit kit by appearance, but rather a design change at some point,
as the exhaust cover on the 71 powerhead has raised bosses for the two damper
mounting points.
Also, as you imply, the clamshell halves have special mounting pins built in for
the dampers to attach to.
I thought about the possibility of installing the Johnson clamshells on the Evinrude,
and it looked promising, until I noticed a big crack in on clamshell by the transom
swivel pin mount.
I’m not sure what was involved in the retrofit vibration damper upgrade,
when it came to attaching them to the exhaust cover and to the clamshells
on each side, nor whether is feasible to mount the dampers from the 71
to the 66 powerhead.
The bottom front motor mount on the 71 looked exactly as the 66, so I guess
there’s nothing wrong with the 66.
1971 port side clamshell with the vibration damper
1966 port side clamshell
1971 powerhead exhaust cover with raised bosses
and special bolts
1966 Powerhead exhaust cover
No raised bosses for damper to mount to, but
perhaps one could use bushings, if the cover
bolt holes are the same, or switch covers.
Prepare to be boarded!